Pesticides, pollution and the lack of protective groves have all contributed to a decline of migratory monarch butterflies.

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By Brian Winter, USA TODAY

A study of beleaguered butterflies in California provides some of the best clues yet as to how other animals may react to climate change, scientists say.

The unprecedented, 35-year analysis of butterfly populations in the Sierra Nevada details how several species are fleeing to higher elevations to escape warming temperatures.

Those butterflies that already live on mountaintops and can't adjust to the heat have "nowhere else to go but heaven," says Arthur Shapiro, a biologist at University of California-Davis who collected the data.

Butterflies have long been regarded as an early warning indicator for climate change. Their short life cycles and high sensitivity to temperature make them especially vulnerable, says Matthew Forister, a biologist at the University of Nevada-Reno and the study's lead author.

"Like polar bears, these high-elevation butterflies were already living in extreme environments, and now they don't have any options" for escape, Forister says. He says butterfly populations have always shifted over time, but the destruction of their habitat has occurred at an accelerated pace in recent years because of urbanization and warming temperatures.

"Their environment is changing so quickly that they just can't cope," Forister says.

The study, published last month in the journal Proceedings of the National Academy of Sciences, tracked 159 species of butterflies at 10 locations. It's one of the best compilations of data on how any species has reacted to environmental changes in recent decades, says Gary Langham, lead scientist in California for the National Audubon Society, a conservation group.

A separate study published in September in Biology Letters said climate change was one possible explanation for a sharp decline in female monarch butterflies in the eastern United States and Mexico. British researchers have tracked a decline in several species of butterflies since the 1960s.

"What's happening to butterflies is an indication of what's happening, and what could happen, to many different kinds of plants and animals," Langham says. "It underscores the importance of protecting habitats."

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